1. Field of The Invention
The subject invention relates to multi-chip modules for switched-mode power supplies.
2. Description of The Related Art
A switched-mode power supply, as disclosed in co-pending U.S. patent application Ser. No. 08/903,779, filed Jul. 31, 1997 (PHA 23,264), assigned to the Assignee of the subject application, includes a controller chip and a switching device for switching the power in a primary winding of a power transformer. In these supplies, the switching device and the controller chip are typically combined in a single encapsulated module, complete with a heat sink. The switching devices are typically vertical diffused MOSFETs (VDMOS) in which the drain is connected to the heat sink. As such, the connections to the various pins of the controller chip and the heat sink act as parasitic capacitors resulting in the application (and withdrawal) of induced currents to and from the pins of the controller chip. Depending on the functions of the affected pins, the operation of the controller chip may be seriously compromised.
One area of concern is the sample-and-hold portion of the controller chip. Co-pending U.S. patent application Ser. No. 08/901,491, filed Jul. 28, 1997 (PHA 23,262), assigned to the Assignee of the present invention, discloses a sample-and-hold circuit for a controller in a switched-mode power supply. In particular, the sample-and-hold circuit is used for sensing the output voltage of the switched-mode power supply and for regulating the switching device in controlling the output voltage. If a too large induced current is injected into the sample-and-hold circuit through an input pin of the controller, the sample-and-hold circuit interprets this induced current as an indication of an over-voltage in the output voltage of the switched-mode power supply. The sample-and-hold circuit then interrupts the switching of the switching device taking the switched-mode power supply out of regulation.